The knowledge of chemical equilibria in {gas-polymer} systems plays an essential role as regards the safety of transport of petroleum products in polymer-made pipes. Thermophysical properties of thermoplastic semi-crystalline polymers are key data for the development of several engineering applications. These applications require the investigation of the behavior of a polymer, in the solid state i.e., between glass-transition temperature T-g and melting-transition temperature T-m, submitted to the triple thermal, barometric, and chemical constraint. The chemical stress results from supercritical fluid sorption. The relatively high temperature and pressure, industrial operating conditions, require for laboratory investigations the use of sophisticated experimental instrumentation in which such extreme conditions can be reproduced. In this context, coupling gas solubility and swelling techniques (VW-PVT) on the one hand, calorimetry and PVT techniques (PCSC) on the other hand, over extended temperature and pressure ranges, provide a wide spectrum of thermophysical and thermomechanical properties like solubility and isobaric thermal expansion, in absence or in presence of solubilized gases. Selected examples taken in the petroleum industry, dealing with different polymers [medium density polyethylene, poly (vinylidene fluoride)] in presence of gases (carbon dioxide CO2, nitrogen N-2), serve to illustrate the importance of gas solubility (VW-PVT) (Boyer and Grolier, Polymer 2005, 46, 3737) data and of heats of interaction (PCSC) measurements (Randzio et al., Fr. Pat. 9109227, Pol. Pat. 295285; Randzio, Chem Soc Rev 1996, 25, 383; Boyer et al., J Polym Sci Part B: Polym Phys 2006, 44, 185) in the broad field of applied polymer thermodynamics. (c) 2006 Wiley Periodicals, Inc.